How do I add a curve fitted plot to this code?

clc 
clear 
close all

xls=xlsread("Exam2_Data.xls"); 
t=xls(:,1); 
y=xls(:,2); 
SST=sum((y-mean(y)).^2); 

for i=1:3
fprintf('For %d order fit\n\n',i);
disp('Polynomial coefficients are');
C=polyfit(t,y,i);
SSR=sum((y-polyval(C,t)).^2);
R2=1-SSR/SST;
fprintf('R^2 is %f\n\n',R2);
end

for i=2:length(t)-1
T=[t(i-1) t(i) t(i+1)];
Y=[y(i-1) y(i) y(i+1)];
  
if(t(i)<33.75&&t(i+1)>33.75)
C=polyfit(T,Y,2);
disp('Value at 33.75 is ');
polyval(C,33.75)
return

end
end

[Rik]

Do you mean like in a live script? Also, are you sure about the return? Don't you mean break? Return causes the current running function to return to the caller, while break causes the current (inner) loop to exit.

[johnmurdock]

I mean I want to add a block of code that plots a curve fitted line with an equation over the data I pulled from excel. I will try break instead of return as well.

Answer 1

[Sambit Senapati]

you can use the polyval and plot functions in tandem to do the job here:

instead of calling polyval(C,33.75) at a single data point, do the following:

>> Y_new=polyval(C,T);

>> plot(T,Y_new)

You could do this for your original data set as well.